We want to check if the results in Table 1 hold up to scrutiny by exploring variations on the analysis. In addition to re-running everything for weekly and daily data, they consider: first shift versus second shift considered separately. For example, see Table 2, which looks at ONE variation: it is JUST LIKE Table 1 except that it considers the first shift and second shift separately. (After Table 1, the authors do not bother to also report the results with a time trend: it doesn't make much difference.)